Interactions between renal medullary blood flow and the diuretic state of the organism will be investigated by measuring erythrocyte velocity in individual vasa recta, and hydrostatic pressures in tubules, vasa recta and collecting ducts with micropipettes. We seek to establish relationships between hydrostatic pressure in tubules and blood vessels, and flow in the blood vessels. The question arises whether diuretic states, which dilate collecting ducts, raise hydrostatic pressure in all medullary structures, and thereby influence medullary blood flow. We plan first to investigate this relationship in animals undergoing saline diuresis to establish pressure flow dynamics. With such patterns in hand, we will then proceed to an investigation of the effects of antidiuretic hormone where a number of anomalous effects await explanation. General systems studies. We are investigating a general systems paradigm arising from hydrodynamics, which suggests that the basis for temporal organization of regulation in physiological control mechanisms involves the operation of nonlinear oscillators characterized as limit cycles. We are currently investigating the presence of low frequency oscillations in arterial blood pressure recordings and the extent to which these oscillations may be modified by variations in dietary salt loads.